* Tipped to raise 450 mln euros a year

* Says expects field to narrow to 19 or 20 bidders

* Auction to start on April 2 and finish by end-April

FRANKFURT, Feb 9 (Reuters) - Forty-five companies have registered to bid for rights to broadcast top-flight German soccer league matches, an auction tipped to fetch a record 450 million euros ($600 million) a season.

The DFL league said its board would decide on Feb. 16 which of the 45 would be allowed to take part.

"I assume that the number of approved bidders will be significantly lower; possibly, it will be at only 19 or 20," DFL head Christian Seifert told journalists on Thursday, without naming any of the companies.

The auction, which is due to start on April 2, will include various packages allowing companies to broadcast soccer matches for four seasons from 2013/14 on television, the Internet or smartphone devices.

It might also pit pay-TV broadcaster Sky Deutschland , the current owner of the live cable rights, against Germany's biggest phone company, Deutsche Telekom.

Phone companies such as Deutsche Telekom and Britain's Vodafone have branched out into providing TV content over German phone lines, challenging cable TV companies such as Kabel Deutschland and Liberty Global's Unitymedia.

Deutsche Telekom owns the online TV rights to Bundesliga and has said it will consider bidding for satellite rights, too.

But Sky Deutschland, whose main draw is the Bundesliga, needs those rights because about half of its 3 million subscribers tune in via satellite.

Also, the 250 million euros it has been paying per season has put a strain on its finances, and analysts have voiced concern it could not afford a bidding war with Deutsche Telekom.

Vodafone has also said it is looking at rights for internet-based TV and mobile devices, and internet group Yahoo! Inc plans to bid for rights to show online highlights of matches.

The Bundesliga's first division is the top league in the world by attendance, drawing more than 42,000 people per league game, according to DFL. The Bundesliga's 18 clubs generated almost 2 billion euros in the 2010/11 season.

A person close to the DFL had said on Wednesday that auctioning the rights could raise as much as 450 million euros a year, up from 412 million in the last auction three years ago.

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